Flange bolt torqueing is an ongoing maintenance issue for companies that utilize a great deal of piping. Piping systems, such as used in chemical processing companies or similar, include a variety of overhead piping and insulated/lined piping which are subject to thermal cycling conditions. Typical flange bolt torqueing for such piping systems includes flat washers on both sides of the pipe flange connection. Tightening the flange bolts usually requires a calibrated torque wrench in order to apply the specified bolt torques (i.e., ft.-lbs. of torque). When anti-seize compounds are used, the torque values can be different. The tightening of the flange bolts with a torque wrench is usually done in a “crisscross” pattern that alternately tightens the bolts located 180° apart. Using this pattern, the bolts are tightened in some percent increment of the desired final bolt torque (i.e., ft.-lbs. of torque) until a majority of the final bolt torque has been achieved. For tightening to the final torque values, the bolts are then sequentially tightened in a clockwise fashion once around the flange. This is done to ensure that the bolts are evenly stressed. Care must be taken to avoid over-torqueing, which can cause damage to any plastic sealing surfaces, liners, plastic flares, and/or plastic faces.
Typically a re-torqueing of the bolts is applied a minimum of twenty four hours after the initial torque or after the first thermal cycle. This re-torqueing allows for seating of the plastic liners and flares and for relaxation of the bolts. Torqueing typically is only done on the system in an ambient, cooled state, and typically never while the process is at elevated temperature.
After the initial torque and re-torque of the bolts, a hydro test can be performed following ANSI requirements. Annual re-torqueing is usually done thereafter, especially if the process lines experience elevated temperatures or extreme ambient temperature situations. Again, annual re-torqueing is typically only done on the system in the ambient or cooled state.
Due to the possibility of mechanical damage to polytetrafluoroethylene (PTFE) flares and/or PTFE-lined piping products, or similar, Belleville springs or disc springs are usually not recommended in the existing flange bolt torqueing systems utilized heretofore. Prior art references do not recommend the use of Belleville springs or disc springs for use with PTFE-lined products.